A thermal printer produces images on a receiver medium by transferring donor material from a donor ribbon to the receiver medium by selectively heating the donor ribbon while simultaneously pressuring the donor ribbon against the receiver medium. In this way, heated donor material transfers from the donor ribbon to the receiver medium to form an image while unheated donor material remains on the donor ribbon. Transfer may be by flow of melted donor material or by movement of sublimated donor material to the receiver medium. The donor ribbon and receiver medium are separated after transfer of the material to yield a receiver medium having a pattern of deposited donor material forming an image.
Donor ribbon is typically connected between a supply spool, which initially carries a supply of unused donor ribbon, and a take-up spool upon which used donor ribbon is wound. In operation, the take-up spool is rotated to draw donor ribbon from the supply spool and across the print head for use in printing. Often the donor spool and take-up spool are joined together by a structural framework to form a thermal donor cartridge. This structural framework positions the supply spool and the take-up spool in a preferred geometric relationship to facilitate proper loading and can also be used to provide surfaces that enclose or otherwise protect the donor ribbon from damage due to incidental contact and from damage due to exposure to contaminants. Such a thermal donor cartridge is disclosed in commonly assigned, co-pending U.S. patent application Ser. No. 11/479,853 filed Jul. 3, 2006 in the name of Lysiak et al.
The cartridge disclosed in the above-mentioned U.S. patent application provides a take-up window between a take-up projection and a main wall of a donor ribbon take-up housing. Because the take-up projection needs to be very thin to meet other design criteria, the take-up projection tends to warp. Sometimes, the direction of warp is towards the main wall of the donor ribbon take-up housing; closing down the take-up window. When this occurs, it creates a donor pinch point during printing. Any such pinch point on the take-up side of the cartridge would cause an unusual gradient in the web tension on the take-up side of the thermal head, tending to result in image artifacts and resulting in user dissatisfaction.
Another potential problem associated with cartridges such as shown in the above-mentioned U.S. patent application pertains to the desire to produce a printer that does not cause unnecessary vibrations. Such vibrations can arise when a receiver material rubs across a lower portion of the take-up projection. The image receiver rubbing on the take-up projection during printing generates a particular vibration due to the flexibility of the guide rib. Such vibration would be considered to be objectionable to many users, and can impact printer performance.